Most soils are unable to supply the amount of nitrogen required to maximise crop yields; nitrogen in the form of fertiliser is added to make up the shortfall. One difficulty that farmers face is how to determine the size and timing of this shortfall and subsequently determine how much and when nitrogen fertiliser should be applied.
Fertiliser decision support systems attempt to address this problem. These systems seek to recommend a schedule of nitrogen fertiliser in the correct timings and amounts to avoid both yield limiting deficits and costly surpluses.
Crops are also sensitive to water deficits. In some climates, summer evapotranspiration substantially exceeds precipitation. In such climates, irrigation is essential to reach yield potentials.
A number of high-value commercial food crops, including but not limited to potatoes, maize and wheat, produce yields that are highly responsive to both irrigation and nitrogen. This has caused a culture of over-irrigating and over-fertilising to ensure valuable yield is not lost due to deficits. This practice wastes fresh water and nitrogen, causes problems with stream and ground water quality, and represents an unnecessary economic cost. In the past farmers have viewed this cost as “insurance” against missing out on potential yield. Rising energy and commodity costs are pushing up the cost of irrigation and fertiliser. At the same time, increasing consumer demand for sustainable production is driving interest and regulation to ensure waste is minimised and the environment is not being damaged.
Currently most farmers irrigate and fertilise according to a recipe based on empirical research (or trial and error) and these recipes often don't provide a very good match with what the crop actually needs.
Current industry standards for scheduling irrigation and nitrogen fertiliser involve monitoring of soil moisture and crop nitrogen status using a variety of techniques. These procedures are reactive, telling the farmer that a crop needs some nitrogen or irrigation today rather than when it will be needed it in the future and how much should be applied. Being able to predict future needs is important because nitrogen can take several days to permeate the soil. If the crop doesn't have enough nitrogen during the period between when it is applied and when it is fully available to the crop, then crop growth will be limited and yield may decline. Predictive methods (such as those used by the invention) are also favourable because they allow forward planning of field operations during the busy growing season.
A number of basic crop and soil models have been published in the literature or are available in the public domain. Crop and soil simulation models use weather data from any location in the world to predict the temperature and solar radiation dependent potential yield and they can predict how much nitrogen and water the soil will provide and how yield will be reduced by water and nitrogen limitations. However, current models do not produce schedules for the application of water and nitrogen that can be easily used by farmers for crop management.